Existing energy production is based largely on combustion of carbon-based fuels derived from coal, crude oil, and natural gas. Although the earth has large deposits of these resources, their use is irreversible. In addition, one of the products of combustion is carbon dioxide, which is currently thought to have negative effects on the earth's climate. Because coal, crude oil, and natural gas have impurities, their refining and use also generate pollutants, most notably mercury (primarily from coal), sulfur oxides, and nitrogen oxides.
Nuclear fission is an alternative source for producing energy. Under normal circumstances, it does not produce carbon dioxide or other air pollutants. However, it does generate dangerous, highly toxic waste that is difficult to manage. In addition, catastrophic failures can render large areas of air, water, and land contaminated and unusable for long time periods, from years to decades.
Renewable energy sources, such as biomass, wind, solar, and geothermal energy, are constantly being replenished or produced in nature. Biomass, wind, and solar energy are all directly or indirectly produced from solar radiation. Geothermal energy is produced by thermal energy stored within the earth. These energy sources are practically inexhaustible. In addition, these energy sources do not inherently generate carbon dioxide or air pollutants by their use. Hence, renewable energy sources are attractive because they can potentially provide a sustainable, clean supply of energy.
Unfortunately, most renewable sources are not available when and where energy is most needed. Currently the only effective means for transporting energy long distances, other than fossil fuels, is as electricity. Existing electricity technology, i.e. batteries, is expensive and even less efficient, and transporting electricity stored in batteries long distances is currently impractical. Therefore, transporting renewable energy is limited by the transmission capabilities of the electric grid. Utilizing renewable energy that is remotely located from areas of greatest demand may not be feasible using processes in the prior art.
Moreover, the times of greatest renewable generation and greatest demand may not be the same. In some cases, the difference in time between greatest renewable generation and greatest demand can be half a year. There may be some means for converting electricity for storage for times this long, but the problem of electrical transmission capacity in real time still applies unless the stored energy can be feasibly be transported. This lack of technically and economically feasible energy conversion and storage for renewable energy, especially for electricity, requires building excess conventional electric-generating capacity that is underutilized to ensure that electric demand is satisfied at all times, while maximizing the use of renewable energy.
In addition, the location, time, and rate of available renewable energy cannot be controlled. For instance, wind and solar power are intermittent and their rate depends on the intensity of wind or solar radiation. Furthermore, the location, time, and rate of energy demand do not generally match that of available renewable energy. For instance, the locations of greatest wind and solar power generation potential are often distant from the locations of greatest energy demand, and the season of greatest renewable energy production is often different from that of greatest energy demand. Therefore, meeting energy demand at all times requires having conventional generation capacity equal to the maximum coincident difference between demand and available renewable energy. When the difference between demand and available renewable energy is less than maximum, which is most of the time, conventional generation capacity will be underutilized.
In some cases, renewable energy cannot be utilized, either because providing enough transmission capacity for peak generation is not economically feasible, or because other sources of generated energy, such as hydro power, must be used instead.
Biomass is biologically produced matter. The chemical energy contained in biomass is derived from solar energy by the natural process of photosynthesis. This is the process by which plants take in carbon dioxide and water from their surroundings and, using energy from sunlight, convert them into carbohydrates. Biomass is, effectively, stored solar energy. However, biomass often decomposes easily and can be difficult to store for long periods of time.
Other energy sources and energy carriers, except fossil fuels, are not storable or are not storable for long periods of time. Nuclear fuels decay over time. Currently, the only practical means for storing electricity is batteries. However, batteries are expensive and inefficient, and only store electricity for a limited time.
Although fuels, biomass, and electricity are transportable, many forms of energy are not feasibly so. In addition, the energy required to transport and distribute energy carriers limits how far and fast they can be transported. Although electricity is transported quickly, transporting it is inefficient. For a form of energy to be practically transportable, it must have both sufficient specific energy, i.e. energy per unit mass, and energy density, i.e. energy per unit volume. Requirements for specific energy and energy density generally depend on the end use of the energy carrier.
Hydrogen (H2) has been proposed as an alternative energy carrier. Unlike electricity, hydrogen can be stored. It can also be transported. Hydrogen releases energy when oxidized to form water. In fact, hydrogen has the greatest heat of combustion per mass (specific energy) of any combustible fuel. In addition, the only product of hydrogen oxidation with pure oxygen is water. Combustion in air may also generate some nitrogen oxides. Unfortunately, hydrogen is the least dense combustible fuel. Consequently, at standard temperature and pressure, its heat of combustion per volume is only a fraction of that for fossil fuels. In fact, the heat of combustion per volume for hydrogen is only about one-third of that for methane, the main component of natural gas. The low energy density of hydrogen precludes its practical use as transportation fuel and limits its use for distributing energy and even for stationary energy storage.
Most of the proposed carbon-neutral energy carriers are hydrocarbons. The synthesis of these compounds from carbon oxide requires hydrogen, which is usually provided by water. Since water is a limited resource in high demand for other uses, the need for water to produce these fuels is a significant drawback with adverse environmental impacts.
In principle, carbon can be produced from virtually any material containing carbon. Carbonaceous materials commonly include fossil resources such as natural gas, petroleum, coal, and lignite; and renewable resources such as lignocellulosic biomass and various carbon-rich waste materials. Solid and liquid feedstocks (whether fossil-based or renewable) can generally be converted to carbon-rich materials by pyrolysis and related processes.
In view of the above-mentioned shortcomings, there are many needs in the art. It is desired to improve upon prior methods of storing and dispatching energy, i.e. to provide a better energy carrier, especially for electrical power generation. It is desired to effectively store electrical energy for electrical load leveling, i.e. to match electrical generation with demand.
It is further desired to increase the utilization of renewable energy sources, especially for electrical power generation, by rendering renewable energy sources storable and dispatchable, thereby decreasing the need for conventional energy sources to meet fluctuating energy demand. Being dispatchable, the energy carrier produced from renewable energy can reduce the need for or even directly replace conventional energy sources.
Commercially, it is desired to decrease the cost of utilizing renewable energy sources, especially for electrical power generation, by decreasing the conventional energy generation capacity required to meet energy demand and/or increasing the utilization thereof. It would be desirable to store and dispatch energy, especially renewable energy, in a way that requires fewer changes to existing transportation and energy generation, transmission, and distribution infrastructure than alternative methods. It would be further desirable to store and dispatch energy, especially renewable energy, in a way that improves on the overall energy efficiency of alternative methods.
It is desired to facilitate distributed electrical power generation. It is further desired to store and dispatch energy in a way that is relatively safe. Additionally, it is desired to store and dispatch energy in a way that effectively recycles the materials used, thereby reducing or eliminating the generation of byproducts with negative environmental impacts, especially carbon dioxide and other greenhouse gases.
Furthermore, it is desired to provide a source of reliable, affordable energy for countries that lack adequate, economical conventional energy sources, but have wind and solar resources.